Chapter 14: Acids and Bases

Acids and Bases are two types of chemical compounds that have a variety of different characteristics and properties

1.1 AcidsAcids are aqueous compounds that tend to donate a H+ ion.

1.1.1 General Characteristics 1. Aqueous solutions of Acids have a sour taste. 2. Acids change the color of acid-base indicators such as pH paper. 3. Some acids react with active metals and release hydrogen gas. For example, Hydrogen gas is formed by the reaction: Mg (s) + H2SO4 gives the products MgSO4 and H2. 4. Acids react with bases to produce salts and water. The salt is an ionic compound. 5. Acids conduct electric current and are referred to as strong or weak electrolytes, depending on the strength of the current conducted.

1.1.2 Acid Nomenclature A binary acid is an acid that contains only two different elements: hydrogen and one of the more electronegative elements. The name of a binary acid begins with teh prefix hydro, the root of the name of the second element follows this prefix, and then the suffix -ic.

Hydrofluoric Acid

An oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, which is usually a nonmetal. For example, HNO3 is an oxyacid.

1.2 Basesare compounds tend to accet an H+ ion.

1.2.1 General Characteristics 1. Aqueous solutions of bases taste bitter 2. Bases change the color of acid-base indicators. 3. Diluted aqueous solutions of bases feel slippery. 4. Bases react with acids to produce salts and water. The properties of a base are neutralized by the properties of an acid and thus dissapear with the additions of an acid to the base. 5. Bases conduct electric currents, and form ions in aqueous solutions and are therefore electrolytes.

1.3 Arrhenius Acids and Bases 1.3.1. OverviewAn Arrhenius acid is a chemical compound that increases the concentration of hydrogen ions, H+, in an aqueous solution. The acid ionizes in the solution, thus increasing the number of ions present. In contrast, an Arrhenius base is a substance that increases the concentration of hyroxide ions, OH-, in aqueous solutions. Some bases release hydroxide ions into the solution while other bases react with water to remove a hydrogen ion, leaving hydroxide ions in the solution.

1.3.2Aqueous solutions of Acids All Arrhenius acids are molecular compounds with ionizable hydrogen atoms. This process occurs when the hydrogen atoms are bonded to highly electronegative atoms that steal the electron out of the hydrogen atom, leaving a H+ ion. All of these are electrolytes in water, in which they are known as aqueous solutions. In water, when the electron is stolen by the highly electronegative element bonded to it, the water molecules attract one or more of the hydrogen ions. This leaves the hydronium ion, H30+ and a negatively charged molecule bonded to a hydrogen, which acts as a base. For example, when HCl is mixed with water, the products H30+ and Cl- are formed.

1.3.3 Strength of AcidsThe strength of acids is determined by the degree that they ionize in an aqueous solution. Strong acids ionize completely, releasing large amounts of hydrogen ions whereas weak acids release comparatively few. 1.3.4 Aqueous Solutions of Bases When bases dissolve in water, they yield the hydroxide ion and the dissociated cation in the ionic compound. For example, NaOH when dissolved in water yields Na+ and OH-. The strength of the base, like that of the acid, depends on the degree of the dissociation of the ions. 1.4.1 Bronsted Lowry Acids and BasesA Bronsted Lowry acid is an molecule or ion that is a proton donor. Because all of these thus donate an H+ ion, all Bronsted Lowry acids are also Arrhenius acids. The difference between the definitions is that Bronsted Lowry acids donate protons to bases. For example, when HCl reacts with NH3, the products NH4+ and Cl- are yielded. Though there is no water involved, the HCl acts as an acid. In this equation, the Cl becomes stable by completing its octet and the NH3 takes the is a extra proton. A Bronsted Lowry base is thus logically a molecule or ion that accepts a proton.

1.4.2Monoprotic and Polyprotic AcidsMonoprotic acids are acids that donate only one proton per molecule. For example, percloric acid, HClO4 and hydrochloric acid, HCl, only can donate one hydrogen atom. For example, when HClO4 combines with water, the products H3O and Cl- are created. HCl only loses one hydrogen and thus is a monoprotic acid. A polyprotic acid on the other hand is an acid that can donate more than one proton per molecule. For example, H2SO4 is a polyprotic acid. H2SO4 is also a diprotic acid because it can donate exactly two hydrogens per molecule. 1.4.3 Lewis Acids and Bases A Lewis Acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond. A Lewis Acid is an atom, ion, or molecule that donates an electron pair to form a covalant bond.

1.5.1 Conjugate Acids and BasesA conjugate base is the species that remains after a Bronsted-Lowry acid has given up a proton. This base is the ion or molecule that can re-accept the proton that has been given up. For example, when HF combines with H2O, F- and H3O+ are formed, of which F- is the conjugate base which can accept a H+ ion to equalize its electrostatic state. The species that is formed when a Bronsted-Lowry base gains a proton is the conjugate acid. In that same example, the H3O+ ion is the conjugate acid because it gives a H+ ion. 1.5.2 Strength of conjugate Acids and Bases The stronger an acid is, the weaker its conjugate base is and the stronger a base is, the weaker its conjugate acid is. For example, when HCl and H20 yield H3O+ and Cl-, Cl- is a weak base because its octet is filled so it has little incentive to take on a H+ ion.

1.6.1 Amphoteric CompoundsAny species that can react as an acid or a base is an amphoteric compound. For example, when Water reacts with sulfuric acid, it acts as a base, Sulphuric Acid but when it reacts with NH3, it acts as an acid.

1.7.1 Neutralization ReactionsBases and Acids neutralize each other by donating/accepting a H+ ion and satisfying both parties. For example, when HCl and NaOH react, the products NaCl and H20 are formed. Neutralization is the reaction of hydronium ions and hydroxide ions to form water molecules. A salt is also produced, which is composed of a cation from the base and an anion from the acid.

1.8.1 Practice Problems

1. Give the name for HI.

2. What kind(s) of acid is H3PO4?

3. In the equation, H2SO4+H2O gives HSO4-+H30, identify the conjugate base and the conjugate acid.

4. Here are two sets of reactants: H2O+ HF and H2O+ KOH. Identify in which water serves as the acid.

5. In the previous problem, what is the name for the H2O atom meaning it can serve as an acid or a base?

6. Is HI polyprotic or monoprotic?

7. What about H2SO4?

8. What is an acid that is a combination of oxygen, hydrogen, and a third element?